The electrical storage battery on a motorized vehicle has historically been a crucial component, the battery being used not only as a source of energy for cranking the vehicle's engine during a startup, but also as a ballast for storing electrical energy, in conjunction with the charging system and voltage regulation circuitry during vehicle operation. The electrical storage battery is sometimes referred to as the Starting-Lighting-Ignition (“SLI”) battery. The on-board SLI battery has to have adequate state of charge for starting the vehicle's engine, in the variety of environmental conditions in which the vehicle is to be operated, including a wide range of temperature extremes.
In modern versions of motorized vehicles, the SLI battery serves the additional function of supplying electrical currents to various systems other than the vehicle's starter motor during start-up. Such systems may include vehicle security systems, which periodically “wake up”, or are called to wake up by the vehicle's operator. Other such systems include keyless remote wireless access devices. In addition, electronic control systems (“ECS”) for engine and accessory management during operation rely on an electrical system featuring an SLI battery. Thus, an SLI battery is desirously of high reliability to ensure proper and complete vehicle design functionality. Hence, failure of the SLI battery may manifest itself in several symptoms, including a vehicle no-start situation.
Battery “parasitic load” is the electrical load presented on a vehicle when the ignition key is in the off position, which load may be constant or intermittent. Excessive parasitic load can drain an SLI battery to a low state of charge (“SOC”) which can prevent the vehicle from being started at a later point in time. Furthermore, a relatively low SOC can be harmful to SLI battery life, especially for batteries which are not designed to tolerate repeated deep charge cyclings. This may be most pronounced in modem vehicles as the number of on-board computer modules which need to wake up periodically during ignition-off situation are increased.
Conditions of excessive parasitic load may in some instances be difficult to detect, since parasitic loads occur during the ignition-off period, and equipment intended to measure parasitic load itself can cause some charge drainage. Excessive parasitic load can also be caused by intermittent unknown faults, including irregularities in module wake up, which can be triggered by specific conditions that may not be readily replicated at-will during an after-the-fact diagnostic attempt. Accordingly, the root cause of excessive parasitic load encountered by an operator in the field may be difficult to reproduce during a service procedure.